1. Field of the Invention
The present invention relates to a medical device for placing an embolic coil at a preselected location within a vessel of the human body, and more particularly, relates to a very small diameter catheter having a distal tip for retaining an embolic coil in order to transport the coil to a preselected position within the vessel and a control mechanism for releasing the embolic coil at the preselected position. This device is particularly suited to transport an embolic coil through the tortuous vasculature of the human brain.
2. Description of the Prior Art
For many years flexible catheters have been used to place various devices within the vessels of the human body. Such devices include dilatation balloons, radiopaque fluids, liquid medications and various types of occlusion devices such as balloons and embolic coils. Examples of such catheter devices are disclosed in U.S. Pat. No. 5,108,407, entitled xe2x80x9cMethod And Apparatus For Placement Of An Embolic Coilxe2x80x9d; U.S. Pat. No. 5,122,136, entitled, xe2x80x9cEndovascular Electrolytically Detachable Guidewire Tip For The Electroformation Of Thrombus In Arteries, Veins, Aneurysms, Vascular Malformations And Arteriovenous Fistulas.xe2x80x9d These patents disclose devices for delivering embolic coils to preselected positions within vessels of the human body in order to treat aneurysms, or alternatively, to occlude blood vessels at a particular location.
Coils which are placed in vessels may take the form of helically wound coils, or alternatively, may be random wound coils, coils wound within coils or many other such coil configurations. Examples of various coil configurations are disclosed in U.S. Pat. No. 5,334,210, entitled, xe2x80x9cVascular Occlusion Assembly; U.S. Pat. No. 5,382,259, entitled, xe2x80x9cVasoocclusion Coil With Attached Tubular Woven Or Braided Fibrous Covering.xe2x80x9d Embolic coils are generally formed of a radiopaque metallic materials, such as platinum, gold, tungsten or alloys of these metals. Often times several coils are placed at a given location in order to occlude the flow of blood through the vessel by promoting thrombus formation at the particular location.
In the past, embolic coils have been placed within the distal end of the catheter. When the distal end of the catheter is properly positioned the coil may then be pushed out of the end of the catheter with a guidewire in order to release the coil at the desired location. This procedure of placement of the embolic coil is conducted under fluoroscopic visualization such that the movement of the coil through the vasculature of the body may be monitored and the coil may be placed in the desired location. With these placements systems there is very little control over the exact placement of the coil since the coil may be ejected to a position some distance beyond the end of the catheter. As is apparent, with these latter systems, when the coil has been released from the catheter it is difficult, if not impossible, to retrieve the coil or to reposition the coil.
Numerous procedures have been developed to enable more accurate positioning of coils within a vessel. Still another such procedure involves the use of a glue or solder for attaching the embolic coil to a guidewire, which is in turn, placed within a flexible catheter for positioning the coil within the vessel at a preselected position. Once the coil is at the desired position, the coil is held in position by the catheter and the guidewire is pulled from the proximal end of the catheter to thereby cause the coil to become detached from the guidewire and released from the catheter. Such a coil positioning system is disclosed in U.S. Pat. No. 5,263,964, entitled, xe2x80x9cCoaxial Traction Detachment Apparatus And Method.xe2x80x9d
Another coil positioning system utilizes a catheter having a socket at the distal end of the catheter for retaining a ball which is bonded to the proximal end of the coil. The ball, which is larger in diameter than the outside diameter of the coil, is placed in a socket within the lumen at the distal end of the catheter and the catheter is then moved into a vessel in order to place the coil at a desired position. Once the position is reached, a pusher wire with a piston at the end thereof is pushed distally from the proximal end of the catheter to thereby push the ball out of the socket in order to thereby release the coil at the desired position. Such a system is disclosed in U.S. Pat. No. 5,350,397, entitled, xe2x80x9cAxially Detachable Embolic Coil Assembly.xe2x80x9d One problem with this type of coil placement system which utilizes a pusher wire which extends through the entire length of the catheter and which is sufficiently stiff to push an attachment ball out of engagement with the socket at the distal end of the catheter is that the pusher wire inherently causes the catheter to be too stiff with the result that it is very difficult to guide the catheter through the vasculature of the body.
Another method for placing an embolic coil is that of utilizing a heat releasable adhesive bond for retaining the coil at the distal end of the catheter. One such system uses laser energy which is transmitted through a fiber optic cable in order to apply heat to the adhesive bond in order to release the coil from the end of the catheter. Such a method is disclosed in U.S. Pat. No. 5,108,407, entitled, xe2x80x9cMethod And Apparatus For Placement Of An Embolic Coil.xe2x80x9d Such a system also suffers from the problem of having a separate fiber optic element which extends throughout the length of the catheter with resulting stiffness to the catheter.
Still another coil deployment system incorporates a catheter having a lumen throughout the length of the catheter and a distal tip for retaining the coil for positioning the coil at a preselected site. The distal tip of the catheter is formed of a material which exhibits the characteristic that when the lumen of the catheter is pressurized the distal tip radially expands to release the coil at the preselected site. Such a deployment system is disclosed in the parent patent application, U.S. patent No. application Ser. No. 09/177,848, filed on Oct. 22, 1998, and entitled, xe2x80x9cEmbolic Coil Hydraulic Deployment System,xe2x80x9d assigned to the assignee of the present patent application.
The present invention is directed toward a very small diameter vascular occlusive coil deployment system for use in placing an embolic coil at a preselected site within a vessel which includes a small diameter, flexible catheter having a distal tip for retaining the coil so that the coil may be moved to the preselected site within the vessel. The catheter has a lumen which extends therethrough the length of the catheter and also includes a distal end which is formed of a material having a durometer such that when a fluid pressure of about 300 pounds per square inch (psi) is applied to the interior of the catheter, the walls of the distal tip expand outwardly, or radially, to thereby increase the lumen of the distal tip of the catheter. The embolic coil is disposed upon and bonded to a cylindrical headpiece which has a diameter approximately equal to the diameter of the lumen of the catheter. The headpiece extends outwardly from the proximal end of the coil and this portion of the headpiece is disposed within and retained by the lumen at the distal tip of the catheter. A hydraulic injector, such as a syringe, is coupled to the proximal end of the catheter for applying a fluid pressure to the lumen of the catheter. When the coil is placed at a desired position within a vessel, fluid pressure is applied to the lumen of the catheter by the hydraulic injector to thereby cause the walls of the distal tip to expand outwardly, or radially, to release the headpiece which carries with it the coil. Most importantly, the diameter of the headpiece is approximately equal to or slightly larger, than the diameter of the lumen of the catheter so that when the headpiece 122 is inserted into the distal section of the catheter, the outside diameter of the attached coil 106 is approximately equal to the outside diameter of the catheter. This construction results in a deployment system having an overall outside diameter approximately equal to that of the catheter.
In accordance with another aspect of the present invention, the flexible catheter is comprised of a proximal section and a relatively short distal section. The proximal section is formed of a material which is sufficiently flexible to be passed through the vasculature of the human body and is of a durometer which essentially resists outward expansion when a fluid pressure on the order of about 300 psi is applied to the interior of the catheter. The distal section of the catheter is formed of a material which is also sufficiently flexible to be passed through the vasculature of the body, yet is of a durometer which is significantly lower than the durometer of the proximal section and exhibits the property of expanding outwardly, or radially, when such a fluid pressure is applied to the interior of the catheter to thereby permit the release of the headpiece to thereby release the embolic coil.
In accordance with still another aspect of the present invention, the distal section of the catheter has a durometer in a range of between about 25D and 55D.
In still another aspect of the present invention, the embolic coil is comprised of a helical coil having a proximal end, a distal end, and a lumen extending therethrough. A headpiece is partially disposed within the lumen of the proximal end of the coil and the other portion of the headpiece is placed in fluid-tight engagement with the lumen of the catheter.
In another aspect of the present invention, the hydraulic injector for applying a fluid pressure to the interior of the catheter takes the form of a syringe which is coupled to the proximal end of the catheter for, upon movement of the piston, creating a fluid pressure which is applied to the interior of the catheter to thereby cause the release of the embolic coil.
In accordance with another aspect of the present invention, the embolic coil may take the form of other types of implantable devices, such as a vascular filter.
These aspects of the invention and the advantages thereof will be more clearly understood from the following description and drawings of a preferred embodiment of the present invention: